I copied this from Tizo's post from =TSF=Since a lot of people here used GIMP I'll post this tutorial.

Here is a tutorial on how to make a grunge orientated background. It could be a small part of your image, or a big part of the image. I hope you enjoy the tutorial!

Step 1: Create a new image. Mine is 323x123, but it really works for any sizes. Go Filters>Render>Clouds>Solid Noise and change the X size into 1 and leave the Y size as is. Confirm and it should look something like this:

Step 2: Next throw on some MetCXChaotix brushes to give the signature a good effect. You could also add some Icytina inksplat brushes now, or later like how I did it. After adding the Chaotix brushes it should look like this:

Step 3: Now go use Colors>Colorize or Color Balance. Depending on which coloring tool you prefer. Now, choose a color that you like or that matches the render you're using:

Step 4: Put your render on your image, add some more or some of your first inksplat brushes. You could find brushes like these and more if you Google it.

Step 5: Now you're all done! Add some of your own personal effects, borders and whatnot into your newly made grunge image and you're done!

Extra: A good text to go well with this grunge style, is called Roteflora. I'm not sure if it's a default text style or not, but again, if you Google it, you might be able to find it somewhere.